Sorry, I just saw Amals reply, I meant to answer this for you yesterday,
As Amal said, the case can cause issues.
A couple of other things to check,
Phone unlocked
NFC turned on
Find the “sweet spot” with xFD and / or diagnostic card (move very slowly, my S9 NFC reads in pulses, 5 low power “reads” then 1 high power “reads”)
Check out the Phone NFC Wiki for some tips and tricks including 3 posts about the Note 10 plus / + and with Otterbox.
Remember, you are trying to make a X or + with you implant antenna crossing the antenna rather than inline with it